1. Field of the Invention
The present invention relates to a polypropylene molded article having a greatly lowered level of odor, and more particularly, it is concerned with a polypropylene molded article suitable for food packaging.
2. Description of the Prior Art
Polypropylene is widely used alone or in the form of blend with other resins to produce film, extruded articles, and injection-molded articles on account of its superior mechanical properties, moldability, and appearance. Unfortunately, molded articles produced from polypropylene have a characteristic odor which poses a serious problem when they are applied to food packaging containers and bags and food storage containers. This odor has an adverse effect on the flavor of foods and deteriorates the value of foods and diminishes the appetite. Therefore, there has been a strong demand for the reduction of this odor.
Possible causes of odors are residues of the volatile solvents (hexane and/or heptane) used in the production of polypropylene, additives (such as antioxidant) in polypropylene, and decomposition products of polypropylene which occur during heating, melting, and molding. These volatile substances stimulate the human's keen sense of smell however small they might be in the molded articles of polypropylene used for food packaging.
There are some known methods of lowering the level of odor by drying polypropylene powder (Japanese Patent Laid-open No. 75410/1980), by using a vented extruder for the pelletization of polypropylene powder and adding a specific additive to polypropylene (Japanese Patent Laid-open Nos. 104145/1985 and 195141/1985). These methods, however, do not provide polypropylene molded articles which have a very low level of odor required for food packaging. To address this problem, the present inventors carried out extensive studies and completed the present invention.